As Creme de Cassis Line bottom of 25 cm round cake pan with parchment or wax paper.Lightly oil pan an dust with cornmeal,shaking out excess.. Sift together cornmeal,flour,baking powder and salt in medium bowl and set aside.. Whisk togethersugar,oil and butter in large mixing bowl until well combined.Add eggs and egg whites,one at a time,stirring until just combined.Stir together yogurt,lemon zest,lemon juice,and lemon extract in small bowl.Fold in dry ingredients until just combined.Do not overmix.. Spoon batter into prepared pan and smooth top with rubber spatula.Bake at 180ºC F until cake is golden and wooden pick inserted into center comes out clean,about 40 minutes.Cool cake on rack 10 minutes.Invert cake onto platter,peel off paper and cool completely.( Cake can be made ahead to this point and refrigerated,wrapped in plastic,up to 3 days.) Toss berries with black currant liqueur.Cut cake into wedges and serve topped with berries.Makes dozen servings.